This invention relates to millimeter waveguide transmission systems utilizing low loss circular electric modes of propagation and, more particularly, to an expansion joint for connecting sections of the waveguide.
Transmission systems employing waveguide which is rigidly supported within a surrounding conduit requires the use of expansion joints to accommodate for expansion and contraction of the individual sections because of variations in temperature. Even systems utilizing compliant continuous supports which may eliminate the necessity of expansion joints between the rigid waveguide sections still require expansion joints for connecting waveguide sections to sensitive repeaters and other termination apparatus.
One expansion joint known in the art utilizes mating tubular sleeves having a slip fit to join the waveguide sections. This prior expansion joint is known to present discontinuities and step functions to the transmitted signals which degrade transmission by generating undesirable spurious modes.
Another known prior expansion joint employs a properly configured dielectric member to transfer a signal across a joint in a trapped mode. This type of expansion joint is complex and, hence, undesirable.
In still another known expansion joint, first and second tubular members are employed which are mounted in a telescoping relationship. A bellows is employed in conjunction with the tubular members to allow variation in the length of the joint in response to thermal expansion and contraction. One problem with such an arrangement is that the bellows is extremely fragile and is easily ruptured. Another problem is the difficulty in manufacturing the bellows to obtain the desired precision needed in most waveguide applications.